Technical Field
The present disclosure is generally directed to super-junction semiconductor devices, and more particularly, to super-junction semiconductor devices capable of operating in Radio Frequency applications.
Description of the Related Art
A wide range of solutions have been developed in recent years to increase the efficiency of semiconductor power devices, in particular, in terms of increasing the corresponding breakdown voltage and reducing the corresponding output resistance.
One such development includes vertical-conduction semiconductor power devices, in which, within an epitaxial layer, which forms part of a drain region having a given type of conductivity (for example a conductivity of an n-type), columnar structures of opposite conductivity (in the example, a conductivity of a p-type) are provided. The columnar structures have a concentration of dopants such as to balance the amount of charge of the epitaxial layer in such a way as to create a substantial charge balance (so-called multi-drain or super-junction technology).
This charge balance enables high breakdown voltages to be obtained, as the value of the breakdown voltage (BV) of a semiconductor device has a maximum at a point corresponding to a perfect charge balance in the corresponding drain layer. In addition, the high concentration of the epitaxial layer enables a low output resistance to be obtained.
Manufacturing of the columnar structures in a standard super-junction semiconductor device may include sequential growth of epitaxial layers, for example of an n-type material, followed by implantation of dopants of an opposite type, e.g., p-type material. The implanted regions are stacked so as to form the columnar structures. Body regions of the super-junction semiconductor device are then provided in contact with the p-type columnar structures, in such a way that the columnar structures constitute an extension of the body regions within the drain region.
While super-junction semiconductor devices have proved useful in some applications, such devices have not been successfully implemented, or even implemented at all, in Radio Frequency (RF) applications.
FIG. 1 is a cross-sectional view of a conventional super-junction semiconductor device 10, as known in the art. The device 10 includes a drift layer 16 that includes alternating columns of p-type and n-type semiconductor material (i.e., p-type columns 15 and n-type columns 17) that are formed on an n-type drain layer 14. P-type body regions 18 are positioned directly on top of respective p-type columns 15, and n-type source regions 20 are formed in respective body regions 18. The device 10 further includes gate electrodes 22 formed over respective n-type columns 17. A plurality of cells 1 (e.g., transistors) are thus formed in the device 10, with each cell 1 including a gate electrode 22 overlying an associated n-type column 17, and source regions 20 formed in adjacent body regions 18 which are in direct contact with respective p-type columns 15. The cells 1 are activated by application of a voltage to the gate electrode 22, which facilitates the flow of a drain-source current (IDS) between the drain layer 14 and the source regions 20, e.g., through the n-type column 17 and associated body regions 18.
The conventional super-junction semiconductor device 10 shown in FIG. 1, while suitable for certain applications, is generally unsuitable for RF applications. That is, for a pre-fixed die size, the implementation of an appropriate RF layout does not constitute necessary and sufficient conditions to ensure the proper working at Radio Frequency of a standard super-junction semiconductor device, since the high intrinsic power density of such super-junction devices would lead to thermal destructive effects at Radio Frequency. For example, using a conventional super-junction semiconductor device (e.g., device 10 of FIG. 1) in RF applications results in the formation of closely packed isotherms (e.g., regions of high current density) in the active n-type columns 17, thereby limiting the effectiveness of such devices in RF applications.